1. Field of the Invention
The present invention relates to an optical waveguide for use in optical communication modules, and a process for producing the same. More particularly, it relates to a three-dimensionally shaped optical waveguide which can be produced by irradiating optical material with light and controlling the refractive index of the optical material, and a process for producing the same.
2. Description of the Related Art
Hitherto, as for optical waveguides which are used to transmit an optical signal in an optical communication module are known a silica-based optical waveguide comprising a cladding part and a core part which are three-dimensionally shaped and formed of silica films which are formed on a quartz glass substrate or silicon substrate by a flame accumulation method, and an optical waveguide comprising a single crystal substrate of lithium niobate as a cladding part, and a core part which is three-dimensionally shaped by thermal diffusion of titanium (Ti) onto the substrate.
However, with respect to the conventional optical waveguides, it is difficult to produce a desired optical waveguide on various kinds of substrates because heat treatment at a high temperature of 1,000xc2x0 C. or more is necessary in the course of the production process thereof. From a standpoint of convenience of production of optical waveguides, instead of the conventional optical waveguides which require such high temperature treatment on production, organic optical waveguides using organic optical material, which can be formed at low temperature, has been studied. The use of organic optical material such as PMMA (polymethyl methacrylate), polycarbonate, polyimide, polysiloxane and BCB (benzocyclobutene) has been studied to produce organic optical waveguides.
The organic optical waveguide is generally produced with the use of organic optical material in such a manner that a lower cladding layer is formed on a silicon or glass substrate, a core layer having a refractive index higher than that of the cladding part is formed, and the core layer is processed by a thin film fine working technique utilizing a dry etching method, such as reactive ion etching (RIE), or a wet etching method using an etchant, to form a core pert, which is thereafter covered with an upper cladding part having a refractive index lower than that of the core part, so as to form a three-dimensionally shaped optical waveguide comprising the cladding part and the core part built therein.
Japanese Unexamined Patent Publication JP-A 6-172533 (1994) proposes a process for producing a polysiloxane series optical waveguide comprising a step of forming a lower cladding layer on a substrate, a step of forming a core part and a step of forming an upper cladding layer, in which the formation of the tote part is conducted by a step of insolubilization of a polymer by irradiation with far ultraviolet rays or an electron beam and a step of removing unnecessary parts.
In the case where the core part is formed by the dry etching on the production of an optical waveguide as mentioned above, complicated and sophisticated processes and their control are necessary when producing a mask pattern and the dry etching method itself needs such processes and their control, and thus there is a problem that a desired optical waveguide cannot be easily obtained. Furthermore, because the processes takes much time and the etching rate of the dry etching is low, there is another problem that a long period of time is required for producing the optical waveguide.
In the case of utilizing the wet etching method as mentioned above, precise control of the processed shape of the core part is difficult because the etching proceeds in an isotropic manner, and thus there is a problem that it is difficult to produce optical waveguides of which processing accuracies of the order of sub-microns are demanded, and functional optical circuits using such an optical waveguide.
In the case of employing the insolubilization step of irradiating a polymer with far ultraviolet rays or an electron beam and the step of removing unnecessary parts as proposed in JP-A 6-172533, the processed shape of the core part can be precisely controlled in comparison with the wet etching using an etchant, and the process becomes convenient in comparison with the case using the dry etching. However, it involves problems that the process is still complicated since the step of removing unnecessary parts is required, and side walls of the core part is roughened in removing unnecessary parts, which causes scattering loss of light.
When a core part of a convex shape is formed, which is then covered with a cladding part as described in the publication, since asperities are formed on the surface of the cladding part, there is a problem that when optical waveguides are accumulated in the vertical direction, the processing accuracy of a core part of an optical waveguide formed by the later step is deteriorated due to the unevenness of the optical waveguide formed by the former step. Therefore, it brings about a problem that loss of light occurs when the light is transmitted through the optical waveguide formed by the later step with low processing accuracy.
The invention has been developed in view of the problems associated with the conventional technologies. An object of the invention is to provide an optical waveguide capable of being produced by an easy process with high productivity and processing accuracy, and a process for producing the same.
The invention provides an optical waveguide comprising:
a core part formed of optical material whose refractive index varies corresponding to an irradiation amount of light having energy higher than that of light to be transmitted; and
a cladding part disposed so as to cover at least part of an outer periphery of the core part in a direction of transmission of light, the cladding part being formed of optical material which is the same material as the core part before irradiation with light, and has a refractive index lower than that of the core part.
According to the invention, the core part and cladding part of the optical waveguide are composed of a layer containing optical material whose refractive index varies corresponding to the irradiation amount of light having energy higher than that of the light to be transmitted. The core part and cladding part are formed by lowering the refractive index of the cladding part in comparison with that of the core part by irradiating the region to be the cladding part with a different amount of light from that of the region to be the core part, so as to provide an optical waveguide comprising the cladding part covering at least part of the outer periphery of the core part in the direction of transmission of light. That is, it is not necessary to use dry etching or wet etching in formation of the core part, and thus the complicated steps and the deterioration of the processed shape associated with the working of the core part using dry etching and wet etching can be eliminated, to provide an optical waveguide produced by an easy process with high productivity and high processing accuracy.
In the optical waveguide of the invention, it is preferable that the optical material of the core part and cladding part has such characteristics that the refractive index decreases with increases in irradiation amount of the light having higher energy within a predetermined range of irradiation amount of light.
The optical waveguide of the invention is characterized in that the core part formed of optical material whose refractive index decreases with increases in irradiation amount of the light having higher energy than that of the guided light, within a predetermined range, is housed in the cladding part formed of the same optical material, having a refractive index smaller than that of the core part by increasing the irradiation amount of the light.
According to the invention, a layer of optical material whose refractive index varies corresponding to the irradiation amount of the light having energy higher than that of the guided light to be transmitted in the core part of the optical waveguide and decreases with increases in irradiation amount of the light within the predetermined range is used in the core part and cladding part of the optical waveguide, and the core part and cladding part are formed by irradiating the region to be the cladding part with a larger amount of the light than that of the region to be the core part, to make the refractive index of the cladding part smaller than that of the core part, so as to provide an optical waveguide comprising the cladding part covering at least part of the outer periphery of the core part in a direction of transmission of light. That is, it is not necessary to use dry etching and wet etching on forming the core part, and thus the complicated steps and the deterioration of the processed shape associated with the working of the core part using dry etching and wet etching can be eliminated, so as to provide an optical waveguide produced by an easy process with high productivity and high processing accuracy.
In the optical waveguide of the invention, it is preferable that the optical material is a material which is converted to a siloxane polymer having siloxane bonds by irradiating the optical material with the light having higher energy.
The optical waveguide of the invention is characterized in that the optical material is a siloxane polymer in which siloxane bonds are formed by the irradiation with light.
According to the invention, the siloxane polymer having a clear relationship, in which the refractive index decreases with increases in irradiation amount of light within the predetermined range of irradiation amount of light, is used, so as to conveniently provide an optical waveguide having a core part and a cladding part which are formed with a desired refractive index.
In the optical waveguide of the invention, it is preferable that a lower limit of the predetermined range of irradiation amount of light is equal to or more than such an irradiation amount that the refractive index of the optical material becomes the maximum with respect to the irradiation with the light having higher energy.
According to the invention, sufficient siloxane bonds are formed in the optical material irradiated with a sufficient irradiation amount of light, to form the optical material wish a firm and stable siloxane polymer, and thus the core part and cladding part having the desired refractive indexes with good weather resistance and heat stability can be formed,
In the optical waveguide of the invention, it is preferable that the light having higher energy is an ultraviolet ray.
According to the invention, since the ultraviolet ray has an effective energy component to a polymerization promoter, the siloxane bonds are formed under good conditions, and an optical waveguide can be provided which is conveniently produced by easily obtaining the desired variation of refractive index.
The invention also provides an optical waveguide comprising;
a substrate;
a first cladding part disposed on one surface of the substrate:
a core part disposed on part of a surface of the first cladding part, opposite to the substrate, the core part being formed of optical material whose refractive index varies corresponding to an irradiation amount of light having energy higher than that of light to be transmitted, and having a refractive index higher than that of the first cladding part;
second cladding parts disposed on remaining part of the surface of the first cladding part, being adjacent to the core part at both aides thereof along a direction of transmission of light, the second cladding parts being formed of the same optical material before irradiation with light, and having a refractive index lower than that of the core part; and
a third cladding part disposed on surfaces of the core part and second cladding parts, opposite to the first cladding part, the third cladding part having a refractive index lower than that of the core part.
According to the invention, even when a plurality of optical waveguides are accumulated in the vertical direction, no asperity is formed on the surface of the respective optical waveguide. Therefore, such problems can be eliminated that the processing accuracy of the optical waveguide formed in the later step is deteriorated due to the unevenness of the optical waveguide formed in the former step, and loss of light occurs in transmitting light in the optical waveguide formed in the later step due to the unevenness.
In the optical waveguide of the invention it is preferable that the first and third cladding parts are formed of optical material whose refractive index varies corresponding to the irradiation amount of the light having higher energy.
According to the invention, since the first and third cladding parts comprise the optical material whose refractive index varies corresponding to the irradiation amount of the light having higher energy, an optical waveguide formed with a desired refractive index can be conveniently provided.
The invention further provides a process for producing an optical waveguide comprising:
a step of forming a layer of optical material whose refractive index varies corresponding to the irradiation amount of light having energy higher than that of light to be transmitted; and
a step of irradiating a region to be a core part and a region to be a cladding part covering at least part of an outer periphery of the core part in a direction of transmission of light, with the light having higher energy in different irradiation amounts, respectively, so as to provide a core part and a cladding part having a refractive index lower than a refractive index of the core part.
According to the invention, the layer comprising optical material whose refractive index varies corresponding to the irradiation amount of light having energy higher than that of the guided light is formed on the substrate, to constitute the core part and cladding part of the optical waveguide. By irradiating a region of the layer to be the cladding part, with light in an irradiation amount different from that for a region of the layer to be the core part, specifically with a relatively large amount of light, to make the refractive index of the cladding part lower than that of the core part, the core part and the cladding part covering at least part of the outer periphery of the core part are formed so as to produce the optical waveguide. That is, dry etching or wet etching is not required on formation of the core part, and the complicated steps and the deterioration of the processed shape associated with the working of the core part using dry etching and wet etching can be eliminated, to produce an optical waveguide by an easy process with high productivity and high processing accuracy.
The process for producing an optical waveguide of the invention is characterized by comprising a step of forming a layer of optical material whose refractive index decreases corresponding to the irradiation amount of light having energy higher than that of the guided light within a predetermined range of irradiation amount of lights and a step of irradiating a periphery of a region of the layer to be a core part, with the light in a relatively large irradiation amount to form the core part and the cladding part having a refractive index lower than that of the core part and housing the core part.
In the process for producing an optical waveguide of the invention, it is preferable that in the step of forming the layer, optical material having such characteristics that a refractive index thereof decreases with increases in irradiation amount of the light having higher energy within a predetermined range of irradiation amount of light is used as the optical material, and
in the step of forming the core part and the cladding part, the region to be the cladding is irradiated with the light having higher energy in an irradiation amount relatively larger than that for the region to be the core part within the predetermined range of irradiation amount of light, to make the refractive index of the cladding lower than that of the core part.
The process for producing an optical waveguide of the invention is characterized by comprising a step of forming a layer of optical material whose refractive index decreases corresponding to the irradiation amount of light having energy higher than that of the guided light within the predetermined range of irradiation amount of light, and a step of irradiating a periphery of a region of the layer to be a core part with the light in a relatively large irradiation amount to form the core part and the cladding part having a refractive index lower than that of the core part and housing the core part.
According to the invention, the layer of optical material whose refractive index varies corresponding to the irradiation amount of light having energy higher than that of the guided light and decreases with increases in irradiation amount of light within the predetermined range is formed on a substrate, and by using the layer as the core part and cladding part of the optical waveguide, the core part and the cladding part covering at least part of the outer periphery of the core part in the direction of transmission of light are formed by irradiating the peripheral region of the core part, i.e., the region to be the cladding part, with light in an irradiation amount relatively larger than the region to be the core part, to make the refractive index of the cladding part smaller than that of the core part, so as to produce the optical waveguide. That is, it is not necessary to use of dry etching and wet etching in formation of the core part, and thus the complicated steps and deterioration of the processed shape associated with the working of the core part using dry etching and wet etching can be eliminated, so as to provide an optical waveguide produced by an easy process with high productivity and high processing accuracy.
In the process for producing an optical waveguide of the invention, it is preferable that in the step of forming the layer, the optical material is a material which is converted to a siloxane polymer having siloxane bonds by irradiation with the light having higher energy.
In the production process described above, the process for producing an optical waveguide of the invention is characterized in that the optical material is a siloxane polymer in which siloxane bonds are formed the irradiation with light
According to the invention, the siloxane polymer having a clear relationship, in which the refractive index decreases with increases in irradiation amount of light within the predetermined range of irradiation amount of light, is used, so as to conveniently provide an optical waveguide having a core part and a cladding part with a desired refractive index.
In the process for producing an optical waveguide of the invention, it is preferable that in the step of forming the layer, a lower limit of the predetermined range of irradiation amount of light is equal to or higher than such an irradiation amount that the refractive index of the optical material becomes the maximum with respect to the irradiation with the light having higher energy.
According to the invention, sufficient siloxane bonds are formed in the optical material irradiated with a sufficient irradiation amount of light, to form the optical material with a firm and stable siloxane polymer, so that the layer having the desired refractive indexes can be formed, and an optical waveguide having good weather resistance and heat stability can also be produced.
In the process for producing an optical waveguide of the invention, it is preferable that the siloxane bonds are formed by irradiation with an ultraviolet ray.
According to the invention, because the siloxane bonds can be formed in good conditions by irradiation with an ultraviolet ray having an effective energy component to a polymerization promoter of siloxane bonds, the desired variation in refractive index can be conveniently obtained, and the optical waveguide can be conveniently produced.